Quill Mites of the Subfamily Syringophilinae (Acariformes: Syringophilidae) Parasitising Starlings (Passeriformes: Sturnidae)

Simple Summary This study provides detailed information on six previously described species of syringophilines associated with starlings and records new host and locality data. Additionally, three new species are described: Aulonastus indonesianus sp. n., Aulonastus anais sp. n., and Syringophiloidus poeopterus sp. n., from various starling hosts across Indonesia, Papua New Guinea, and Tanzania. The study reveals that species from the genera Syringophiloidus and Syringophilopsis exhibit a broad host range among passerine birds, suggesting a long-established symbiotic relationship before the global dispersal of starlings. In Europe, the Eurasian Starling hosts Krantziaulonastus, while in Africa, related niches are occupied by Picobiinae mites. The research highlights the intricate coevolutionary dynamics between quill mites and their avian hosts. Abstract Quill mites of the family Syringophilidae are widely distributed parasites of birds inhabiting the interior of feather quills. In this paper, we provide detailed information on the host spectrum and distribution for six previously described species of syringophilines associated with starlings with new host and locality records. Additionally, we describe three new species: Aulonastus indonesianus Marcisova, Skoracki, and Patan sp. n. from the Common Hill Myna Gracula religiosa Linnaeus in Indonesia (Java) and the White-necked Myna Streptocitta albicollis (Vieillot) in Indonesia (Celebes); Aulonastus anais Skoracki and Patan sp. n. from the Golden Myna Mino anais (Lesson) in Papua New Guinea; and Syringophiloidus poeopterus Skoracki and Patan sp. n. from the Abbott’s Starling Poeoptera femoralis (Richmond) in Tanzania. Finally, we explore the host–parasite interactions within the system comprising starlings and syringophiline mites.


Introduction
Mites of the family Syringophilidae Lavoipierre, 1953, belong to widely distributed parasites of birds, spending their entire lives inside feather quills.In this unique habitat, they feed, undergo their entire development, and copulate [1][2][3][4][5].The dispersing forms are adult fertilised females, which move to a new host during the breeding season, from parents to offspring (vertical transfer).Horizontal transfer of parasites can also occur during host mating or through frequent contact between host individuals, especially among social birds or between predators and their prey [6][7][8][9].The infestation rate of the host population by Syringophilidae mites is undoubtedly dependent on the host's behaviour; it is relatively high in social species (reaching up even to 70%) and low in solitary species [10][11][12][13].It is worth noting that in the field studies provided in Poland, the examined population of the Eurasian Starling was infested by quill mites on a quite high level (the prevalence = 54%) [14].
Syringophilids, living and feeding on the tissue fluids of birds, are not considered to significantly reduce bird fitness [15].However, our understanding of the harm caused by syringophilids is still incomplete.Veterinarians have observed clinical symptoms of feather picking in domestic birds attributed to quill mites, as reported in various studies [16][17][18].Gritschenko [19] suggested that S. bipectinatus feeding induces itching, leading chickens to peck at affected feathers.This behaviour was thought to cause feather loss due to muscle tone relaxation, allowing new feathers to displace old, infested ones.Despite these findings, recent research shows no signs of quill mites causing skin or feather morphological changes in wild birds, even under heavy infestation [13][14][15].On the other hand, the studies provided by Skoracki et al. [20] suggest that quill mites could act as vectors for the bacterium Anaplasma phagocytophilum, an obligate intracellular pathogen.These studies specifically found this pathogen in syringophiline mites, parasitising Eurasian Starling (Sturnidae) and Blackbirds (Turdidae).From an epidemiological perspective, the vertical transmission of syringophilids could potentially accelerate the spread of various avian diseases within bird populations.Since then, several other symbionts have been identified in quill mites, including multiple genetically distinct lineages of Wolbachia [21] and Spiroplasma [22].
The family Syringophilidae is divided into two subfamilies, Syringophilinae and Picobiinae, significantly differing from each other in terms of morphology, biology, and ecology [2,4,23].Mites from the Syringophilinae subfamily, the subject of this article, exhibit high specificity towards their host groups.Each mite species typically parasitises a narrow host range, usually confined to hosts within a single order.For example, Aulobia and Syringophilopsis are found exclusively in birds of the order Passeriformes, while Syringophilus and Colinophilus parasitise Galliformes, and Creagonycha and Niglarobia are associated with Charadriiformes [4,5].Additionally, Syringophilinae species are specific to the type of feather they inhabit.For instance, Syringophiloidus prefers secondary feathers, Syringophilopsis is found in primary and secondary feathers, Neoaulonastus inhabits secondary feathers and coverts, and Aulonastus occupies coverts and contour feathers [2,4,5].
The Syringophilinae subfamily currently includes 328 species grouped in 50 genera [24,25].They have been found on host representatives belonging to many orders of neognathous birds (Neognathae), whereas in paleognathous birds (Paleognathae), they are known only among representatives of the Tinamiformes order.However, Skoracki et al. [26] suggest that their presence as representatives of this order is the result of a switch from hosts belonging to neognathous birds.The Passeriformes order has its own syringophiline fauna grouped into 12 genera [2,4,5].Among this diversity, four genera of syringophilines have been recorded from starlings so far.In this paper, we provide detailed information on the host spectrum and distribution for all described species of syringophilines with new host and locality records.Additionally, we describe three new species within the genera Aulonastus and Syringophiloidus collected from starlings captured in Indonesia, Papua New Guinea, and Tanzania.

Materials and Methods
The mite material used in the present study was collected from dry bird skins housed in the ornithological collection of the Bavarian State Collection of Zoology, Munich, Germany (Staatliche Naturwissenschaftliche Sammlungen Bayerns SNSB-ZSM).Overall, we examined 44 species belonging to the family Sturnidae, of which only nine were infested by syringophiline mites, i.e., Ampeliceps coronatus Blyth, Gracula religiosa Linnaeus, Mino anais (Lesson), Notopholia corrusca (Normann), Onychognathus morio (Linnaeus), O. nabouroup (Daudin), Poeoptera femoralis (Richmond), Sarcops calvus (Linnaeus), and Streptocitta albicollis (Vieillot).From each infested individual, we collected one wing covert and 4-5 upper and under tail coverts.Mites were removed from wing covert and under-tail coverts using sharp tweezers.Before mounting, specimens were softened and cleared in Nesbitt's solution at room temperature for three to four days, according to the protocol introduced by Krantz and Walter [27] and Skoracki [4].
Identification of mite specimens and drawing preparations were carried out with a light microscope (ZEISS Axioscope2™, Oberkochen, Germany) with differential interference contrast (DIC) optics and a camera lucida.All measurements in the descriptions are given in micrometres.The nomenclature for the idiosomal setation follows Grandjean [28], as adapted for Prostigmata by Kethley [29], leg setation is that of Grandjean [30], and general morphological terms follow Skoracki [4].
Specimen depositories are cited using the following abbreviations: AMU-Adam Mickiewicz University, Department of Animal Morphology, Pozna ń, Poland; SNSB-ZSM-Bavarian State Collection of Zoology, Munich, Germany.
The common and scientific names of birds are after Clements et al. [31] and del Hoyo et al. [32].Zoogeographical regions are after Holt et al. [33] and Ficetola et al. [34].Female, holotype (Figures 1 and 2A-C).The total body length is 530 (555-595 in 45 paratypes).Gnathosoma.The infracapitulum is apunctate.Movable cheliceral digits are 130 (130-135) long.The stylophore is 175 (170-185) long, and the exposed portion of the stylophore is apunctate and 130 (130-140) long.Each medial branch of the peritremes has two chambers, and each lateral branch has seven chambers (Figure 2A).Idiosoma.The propodonotal shield is well sclerotised, apunctate, bearing bases of setae ve, si, and c1, and the margin between bases of setae se and c1 is indistinct.Bases of setae c1 are situated slightly posterior to the level of setal bases se.Propodonotal setae ve and si are short and subequal in length.The hysteronotal shield is absent.Bases of setae d1 are situated closer to d2 than to e2.Setae c1 are about 1.5 times longer than c2.Setae d2 are distinctly longer than d1 and e2.The pygidial shield is apunctate and has a rounded anterior margin.The genital plate is absent.Genital setae g1 and g2 and pseudanal setae ps1 are equal in length.Coxal fields I-II are well sclerotised, III-IV weakly sclerotised, and all apunctate.Body cuticular striations as in Figure 1

Differential Diagnosis
Aulonastus indonesianus sp.n. is morphologically similar to the recently described Aulonastus darwini Skoracki, Sikora, Unsoeld and Hromada, 2022 collected from two host species of the genus Geospiza (Thraupidae) [35].In females of both species, the infracapitulum is apunctate; setae ve and si are subequal in length; setae c1 are longer than se; the genital plate is absent; fan-like setae have six or seven tines, and all coxal fields are apunctate.This new species differs from A. darwini by the following features: in females of A. indonesianus, the stylophore is 170-185 long; each lateral branch of the peritremes has seven chambers; the propodonotal shield bearing bases of setae ve, si and c1; bases of setae c1 are situated slightly posterior to level of setal bases se, and the hysteronotal shield is absent.In females of A. darwini, the stylophore is 130-135 long; each lateral branch of the peritremes has four or five chambers; the propodonotal shield bearing bases of setae ve, si, se and c1; bases of setae c1 and se are situated at the same transverse level, and the hysteronotal shield is present and fused with the pygidial shield.

Etymology
The name "indonesianus" is taken from the region where the hosts were captured-Indonesia.
Female, holotype (Figures 3 and 4A-C).The total body length is 590 (550-600 in 11 paratypes).Gnathosoma.The infracapitulum is densely punctate.Movable cheliceral digits are 120 (120-125) long.The stylophore is 170 (165-170) long; the exposed portion of the stylophore is apunctate and 130 (125-130) long.Each medial branch of the peritremes has one or two chambers, and each lateral branch has four chambers (Figure 4A).Idiosoma.The propodonotal shield is well sclerotised, bearing bases of setae ve, si and c1, sparsely punctate near bases of setae ve and si, and the margin between bases of setae se and c1 is indistinct.Bases of setae c1 and se are situated at the same transverse level.Propodonotal setae ve and si are short and subequal in length, or setae si are slightly (1.3 times) longer than ve.Bases of setae d1 are situated closer to d2 than to e2.Setae c1 are 1.5 times longer than c2.Setae d2 are distinctly longer than d1 and e2.The hysteronotal shield is narrow and apunctate, not fused with the pygidial shield, situated between bases of setae d1 and e2.The pygidial shield is apunctate and has an indistinct anterior margin.The genital plate is absent.Genital setae g1 and g2 are equal in length.The coxal fields I-II are well sclerotised, III-IV weakly sclerotised, all punctate.Body cuticular striations as in Figure 3.   Male.(Figure 4D,E).The total body length is 380 in one paratype.Gnathosoma.Infracapitulum is apunctate.The stylophore is 135 long; the exposed portion of the stylophore is with striae ornament and apunctate and is 110 long.Each medial branch of the peritremes has three chambers, and each lateral branch has five or six chambers (Figure 4D).Idiosoma.All dorsal shields are weakly sclerotised and apunctate.The propodonotal shield is trapezoidal in shape, bearing bases of setae ve, si and c1.Setae ve and si are subequal in length.Bases of setae c1 and se are situated at the same transverse level.The hysteronotal shield is fused to the pygidial shield; the anterior margin is concave and reaches the level of setal bases d1.d1, d2 and e2 are subequal in length.Setae h2 are about three times longer than f2.Coxal fields are weakly sclerotised and apunctate.Body cuticular striations as in Figure 4E.

Type Material Deposition
The holotype and most paratypes are deposited in the SNSB-ZSM, except five females and one male in the AMU.

Differential Diagnosis
This new species is morphologically similar to the above described species, A. indonesianus, and can be easily distinguished by the following features: in females of A. anais, the infracapitulum is densely punctate; each lateral branch of the peritremes has four chambers; bases of setae c1 and se are situated at same transverse level; the hysteronotal shield reduced to small and narrow shield, situated between bases of setae d1 and e2; and all coxal fields are punctate.In females of A. indonesianus, the infracapitulum is apunctate; each lateral branch of the peritremes has seven chambers; bases of setae c1 are situated slightly posterior to the level of setal bases se; the hysteronotal shield is absent; and all coxal fields are apunctate.

Etymology
The name "anais" is taken from the species name of the host, Mino anais.Female, holotype (Figures 5 and 6A).The total body length is 675 (620-670 in three paratypes).Gnathosoma.The infracapitulum is apunctate.The stylophore has a length of 160 (155-160), and the length of the exposed portion of the apunctate stylophore is 130 (125-130).Each medial branch of the peritremes has two chambers, and each lateral branch has ten chambers (Figure 6A).Idiosoma.The propodonotal shield is well sclerotised, rectangular in shape, and sparsely punctate between bases of setae ve and si.Propodonotal setae vi, ve, and si are short, smooth, and subequal in length.Bases of setae c1 and se are situated at the same transverse level.The hysteronotal shield is well sclerotised and apunctate; the anterior margin reaches above the level of setal bases d2, and the posterior margin is not fused to the pygidial shield and not reaching bases of setae e2.Bases of setae d1 are situated closer to d2 than to e2.Setae d1, d2, and e2 are subequal in length.The pygidial shield is apunctate and with rounded anterior margin.The genital plate is absent.(35)(36)(37)(38)(39)(40), and l'RIV 25 (25).
Male (Figure 6B-E).The total body length is 475-560 in two paratypes.Gnathosoma.The infracapitulum is apunctate.The stylophore has a length of 160 (155-160), and the exposed portion of the stylophore is apunctate and 135-145 long.Each medial branch of the peritremes has two or three chambers, and each lateral branch has ten chambers (Figure 6B,C).Idiosoma.The propodonotal shield is well sclerotised, rectangular in shape, and sparsely punctate between bases of setae ve and si.Propodonotal setae vi, ve, and si are short, smooth, and subequal in length.Bases of setae c1 are situated posterior to the level of setae se.The hysteronotal shield is well sclerotised, large, and punctate, the anterior margin reaching above the level of setal bases d2, the posterior margin is not fused to the pygidial shield and reaching bases of setae e2.Bases of setae d1 are situated closer to d2 than to e2.Setae d2 are 2.5 times longer than d1 and e2.The pygidial shield has indistinct anterior margin.Agenital setae ag1 are 1.4 times longer than ag2.The body cuticular striations as in

Types Deposition
Holotype deposited in the SNSB-ZSM, paratypes in the AMU.

Etymology
The name "poeopterus" is taken from the generic name of the host, Poeoptera.
The world fauna of quill mites of the subfamily Syringophilinae associated with Starlings is summarised in Table 1.

Discussion
The bird family Sturnidae (Starlings and Mynas) includes approximately 125 species divided into 36 genera [42].Their distribution is confined to the Old World, naturally occurring in Europe, Asia, Africa, northern Australia, and the Pacific islands, except for anthropogenic introductions and/or invasions in regions such as New Zealand and both Americas.The centres of biodiversity of this family are identified in Southeast Asia and Africa [42,43].Our study has identified four genera of quill mites belonging to the subfamily Syringophilinae, which are prevalent across a wide array of passerine birds.
Mite species belonging to the genus Syringophiloidus have been recorded on hosts across 22 passerine families [4,44,45].Currently, we have recorded four species residing on starlings observed across the Oriental, Palearctic, and Ethiopian regions, as well as on both basal and crown starling lineages [43].This pattern suggests that the genus Syringophiloidus established a symbiotic relationship with starlings prior to their worldwide diversification, likely during the Miocene period [46,47].
Similarly, species from the genus Syringophilopsis predominantly inhabit passerine birds, having been documented in up to 27 families [44].Although two species from this genus have only been recorded on starlings occurring in the Ethiopian and Palaearctic regions, the absence of records from the Oriental region may be due to insufficient specimen examination.It is conceivable that future research will uncover the presence of this genus in the Oriental region as well.Similar to Syringophiloidus, it is plausible that Syringophilopsis established its association with starlings before their global dispersal.
The distribution of mites from the genera Aulonastus (two species) and Krantziaulonastus (one species) presents a notable scenario.Representatives of the genus Aulonastus are found in the body feathers of the rather basal Asian jungle starlings' lineage in the Oriental region [43].In contrast, in Europe, the Eurasian Starling (Sturnus vulgaris), a member of the Eurasian savannah starlings' clade, hosts a member of a different genus, Krantziaulonastus, occupying the same ecological niche.Interestingly, neither of these syringophiline genera has been recorded in Africa, where different crown starling clades have diversified.However, syringophilids belonging to the subfamily Picobiinae occupy their body feather quills, utilising the same niche.

Conclusions
Our study identified the presence of nine mite species belonging to four genera of the subfamily Syringophilinae.Our dataset elucidates the host specificity of these quill mite species, revealing a combination of mono-and oligoxenous tendencies.The latter are consistently restricted to hosts from specific zoogeographical regions and infest closely related genera.This specificity indicates a nuanced symbiotic relationship between quill mites and their avian hosts, likely shaped by intricate coevolutionary dynamics.In conclusion, our research not only enhances the knowledge of quill mite diversity and host specificity but also underscores the importance of continued studies to gain a more comprehensive understanding of the ecological and evolutionary aspects of these symbioses.Through this research, we gain a better understanding of how quill mites adapt to their hosts and how these interactions can influence biodiversity and ecosystem functioning.

Figure 4 .
Figure 4. Aulonastus anais Skoracki and Patan sp.n., female (A-C), male (D,E).(A)-peritremes; (B)-fan-like seta p'III; (C)-solenidia of leg I; (D)-peritremes; (E)-body in dorsal view.Scale bars: (A-D) = 20 µm, (E) = 50 µm.Male.(Figure4D,E).The total body length is 380 in one paratype.Gnathosoma.Infracapitulum is apunctate.The stylophore is 135 long; the exposed portion of the stylophore is with striae ornament and apunctate and is 110 long.Each medial branch of the peritremes has three chambers, and each lateral branch has five or six chambers (Figure4D).Idiosoma.All dorsal shields are weakly sclerotised and apunctate.The propodonotal shield is trapezoidal in shape, bearing bases of setae ve, si and c1.Setae ve and si are subequal in length.Bases of setae c1 and se are situated at the same transverse level.The hysteronotal shield is fused to the pygidial shield; the anterior margin is concave and reaches the level of setal bases d1.Setae d1, d2 and e2 are subequal in length.Setae h2 are about three times longer than f2.Coxal fields are weakly sclerotised and apunctate.Body cuticular striations as in Figure 4E.Legs.The fan-like setae of legs III and IV have five or six tines.Lengths of setae: ve 10, si 10, se 25, c1 45, c2 25, d1 10, d2 15, e2 10, f2 15, and h2 50.Type Material